I live in the dry rain forest of northern Guanacaste, Costa Rica. We endure 4-5 months without rain and many of the trees lose their leaves during this "dry season". The landscape turns gray/Brown. My question is this. A month or so before the first rain the trees begin to show signs of leafing, their green begins to return without any rainfall. The biology teacher here believes it is because the trees are beginning to die and are leafing in a last gasp effort at survival. I had always thought that this was a form of cyclical/learned behavior in that the trees were accustomed to the regularity of the dry and wet season and began to leaf in the "knowledge" that rain would soon follow. Which is it or are other factors involved.Thank You sincerely,Rodgers Bestgen

Well, I can tell you one thing, the tree ain't dieing. It could be a mechanism analogous to vernalization as Cat said. It could be some sort of internal rhytm of the tree. It could be sensing the amount of day light - case in which some light-sensing proteins need be involved. Phytochrome or Zeit Lupe are my two best guesses in this last case. Without actually studying the tree, we can only take educated guesses. But I'm pretty sure the tree ain't dieing.

"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

The effect seems to take place with everything from the Guanacaste tree for which the region is named and teak trees which are farmed in the are. Many other tropical hardwoods as well as most deciduous tropical species.